I have what I am told is a very unusual M1. It is a Springfield with serial number 1986xxx. It is in excellent condition. This one that has even stumped my local expert. It is quite obviously an M1 Garand is styling, it is the length of a Tanker model however it is chambered for .308 (7.62) and has a detachable box magazine.

I bought the gun 10+ years ago off an old Range Master that was retiring. The story he told me was that it was a late war prototype that never went into production but instead turned into the M14.

Above serial number on receiver is marked:
U.S. RIFLE
CAL. 30M1
SPRINGFIELD
ARMORY

When charging handle is pulled back you can see the marking 4 * 4 4 44 on the barrel.
Top front of bolt marked D6528287 HRA and a U under that number.
Front of handgrip marked P (may be underlined) and bottom of handgrip marked RA - P

Rick, I strongly encourage you to field these questions over at the CMP.org forum. The wealth of historical knowledge, expertise and experience of the members over on that forum regarding the M1 Garand is relatively astounding.

I'm personally aware that a very few custom gunsmiths that offer the service of converting an M1 Garand into a magazine fed rifle. . . but what you've conveyed regarding your understanding of the history of your M1 specimen, well. . . only the guys over at the CMP would genuinely know.

Your rifle is a conversion and not original. There have been several commercial conversions offered over the years. Detachable mag or .308 M1 Garands have never been produced by USGI.
Some of the conversions worked real good and others are jam-o matics,